The present invention relates to an actuator which is adapted to be actuated by pressurized fluid and includes a plurality of interconnected pistons and cylinders.
Federal Republic of Germany 36 32 355 A1, commonly owned with the present application, discloses an actuator adapted to be actuated by pressurized fluid, which has piston-cylinder units arranged one behind the other, the pistons and the cylinders of adjacent units being combined to form one part. In this actuator, the manufacture of the parts which interconnect the pistons does not present any substantial difficulties. However, the manufacture of the parts which interconnect the cylinders can be effected only at relatively high expense. This is due to the large number of parts required, the control of the tolerances as to position and shape, the required quality of manufacture with respect to certain dimensions, the cost of the cylindrical tubes, and the relatively high cost of assembly of the parts.
Furthermore, the seal used in this construction unfavorably leads away from a compact structural shape, since such seals must be increasingly thicker and stabler with increasing piston-cylinder diameters and increasing operating pressures of the pressure fluid.
Finally, the reliability in operation of the actuator is also impaired as a result of the parts which are each composed of a plurality of individual parts. The patent refers to the design of the multiposition cylinder to the effect that several of its parts are to be developed as injection moldings which can be produced at favorable price. However, this does not award the difficulties with respect to the seal separating the cylinders.
The article "Hydraulic Digital Actuator", in Control Engineering, February 1965, pages 69 and 70, discloses an actuator operable by pressurized fluid in which a plurality of pistons are displaceably contained within a cylindrical tube. In order to establish different operating stroke lengths, each of the pistons is developed with a recess at one end and with a T-shaped extension at the other end. The manufacture of such pistons involves considerable expense due to the considerable amount of necessary machining work and due to complicated shapes in the manufacture by injection molding. Furthermore, this construction results in an actuator of excessive length.
Also of interest is GB 2,092,229 which discloses a pressure-fluid-operated positioning device having cylinders arranged in series and pistons and floating pistons movable therein between stops which are movable from the outside. Due to the arrangement of end plates closing the cylinders and the floating intermediate pistons, the device requires a considerable number of seals, which negatively affect its reliability. Furthermore, the length added by the end parts and the stops prevents the device from being relatively compact and from having a short overall length.
The disclosures of these and all other prior art materials mentioned herein are expressly incorporated by reference.